ANSWER:uClinux is a set of patches for linux to allow it to run on systems without an MMU (memory management unit). It does not remove any of the support for systems with an MMU, so you can still use your uClinux kernel source on systems with an MMU.
Some portions of the uClinux patches are uClinux specific. For example the flat file loader is unlikely to compile/work on a system with an MMU. But this is the exception rather than the rule.
It is possible to port uClinux to systems with an MMU but run with the MMU disabled, in this case the system will behave just like a true uClinux system.